I doubt that the old MagSafe chargers are capable of outputting the variety of voltages necessary to be usefully compliant with USB-C charging. IIRC, the old MagSafe chargers put a fairly small voltage on their output pins, and when a load was detected they turned on the full voltage and power—but there was no real data communication between the computer and the brick (just between the computer and the connector at the end of the charging cable). USB-PD however is a complicated protocol.
